Engine exhaust gas additive storage system

ABSTRACT

System for storing an internal combustion engine exhaust gas liquid additive, the said system comprising a tank for storing the additive and an “immersed” baseplate ( 1 ) positioned through an opening made in the bottom wall of the tank, the said baseplate comprising at least one orifice through which a system for injecting the said additive into the exhaust gases can be fed, and also incorporating at least one other active component of the storage system and/or of the injection system.

The present application relates to an engine exhaust gas additivestorage system.

Legislation concerning emissions from vehicles and heavy goods vehiclesstipulate, among other things, a reduction in the amount of oxides ofnitrogen NO_(x) discharged into the atmosphere. One known way to achievethis requirement is to use SCR (selective catalytic reduction) whichallows for reduction of the oxides of nitrogen by injecting a reducingagent, generally ammonia, into the exhaust system. This ammonia mayoriginate from the thermolytic decomposition of a solution of an ammoniaprecursor, the concentration of which may be the eutectic concentration.An ammonia precursor such as this is generally a solution of urea.

Using the SCR method, the high levels of NO_(x) produced in the engineduring combustion at optimized efficiency are treated in a catalyticconverter as they leave the engine. This treatment requires the use ofthe reducing agent at a precise concentration and extreme quality. Thesolution is thus metered accurately and injected into the exhaust gasstream where it is hydrolysed before converting the oxide of nitrogen(NO_(x)) into nitrogen (N₂) and water (H₂O).

To do this, it is necessary for the vehicles to be equipped with a tankcontaining a solution of additive (generally urea) and with a device formetering and injecting the desired amount of additive into the exhaustsystem.

Various systems for storing and feeding reducing additives have beenprovided in the prior art, and these can be split roughly into twocategories: those which withdraw the required amount of additivedirectly (and which therefore do not recirculate the additive solution)and those which do recirculate the additive solution.

In the 1^(st) case, the metering device (which may be a pump or ametering valve) can be fed with additive simply under gravity, via aline starting in the bottom of the storage tank. U.S. Pat. No. 5,628,186describes a system such as this.

In the 2^(nd) case, where the outward and return flows are generallycontrolled using a pressure regulator, the additive is metered underpressure and recourse is generally had to a pump for generating thispressure. U.S. Pat. No. 6,063,350 describes a system such as this.

In order to be able to meter the solution of additive correctly into theexhaust gases, it is known practice to incorporate into the additivetank elements such as a level gauge, a temperature sensor, a qualitysensor, a resistive heating element, etc. The aforementioned patent U.S.Pat. No. 6,063,350 proposes to group these various components togetherin the baseplate of the pump, positioned on the top wall of the tank.This approach makes it easier to incorporate the system into the vehicle(as all the connections are grouped together in the same place) andmakes it possible to reduce the number of openings made in the wall ofthe tank. However, the fact that the baseplate is situated on the topwall of the tank has numerous disadvantages:

-   there are high points in the feed and return lines, where there is a    risk that the gases resulting from a possible decomposition of the    additive may accumulate;-   it becomes necessary to provide a trap to prevent the pump from    running dry and losing its prime;-   gauging becomes somewhat inaccurate as a result of deformation of    the end wall of the tank over the course of its life;-   the components suffer prolonged exposure to additive vapours, even    though these vapours are often corrosive (ammonia is present in the    case of urea);-   some components may become damaged in the event of freezing, because    lumps of solid additive floating at the surface may, as they move    around, strike the said components.

The present application is aimed at providing an engine exhaust gasadditive storage system that makes it possible to reduce or evencompletely avoid the aforementioned disadvantages.

To this end, the present invention relates to a system for storing aninternal combustion engine exhaust gas liquid additive, the said systemcomprising a tank for storing the additive and an “immersed” baseplatepositioned through an opening made in the bottom wall of the tank, thesaid baseplate comprising at least one orifice through which a systemfor injecting the said additive into the exhaust gases can be fed, andalso incorporating at least one other active component of the storagesystem and/or of the injection system.

The term “bottom wall” is in fact, in the context of the invention,intended to denote the bottom half of the tank (whether or not it ismoulded in one piece or from two sheets or parison halves). As apreference, the baseplate is located in the bottom third of the tank,and as an especial preference, in the bottom quarter, or even actuallyin the bottom of the tank. It may be partially situated on the bottomside wall, in which case it is at a slight angle once it is mounted inthe vehicle. The location and/or direction of the baseplate depends inparticular on the location of the tank within the vehicle, and on thespace around it (given the components that need to be incorporated intoit).

The additive to which the invention relates is an additive that isliquid under normal conditions of use. It is preferably a reducing agentcapable of reducing the NO_(x) present in the exhaust gases of internalcombustion engines. It is advantageously a solution of a precursor whichgenerates ammonia (the actual reducing agent) in situ, within theexhaust gases. The invention yields good results with urea as aprecursor and, in particular, with aqueous solutions of urea. Eutecticsolutions (containing 32.5 wt % of urea) are highly suitable. It must,however, be noted that these freeze at around —11° C. and that it istherefore advantageous to equip the system with a heater to guardagainst freezing, this heater advantageously being incorporated into thebaseplate according to the invention (see later).

The present invention may be applied to any internal combustion enginelikely to generate NO_(x) in its exhaust gases. This may be an enginewith or without a fuel return line (that is to say a line returning anysurplus fuel not used by the engine to the fuel tank). It isadvantageously applied to diesel engines and, in particular, to dieselengines of vehicles and, as an especial preference, to the dieselengines of heavy goods vehicles.

The system according to the invention comprises at least one tankintended to store the additive. This tank may be made of any material,preferably one which has chemical resistance to the additive concerned.This will generally be a metal or a plastic. In the case of urea,polyolefin resins, particularly polyethylene (and more particularly,HDPE or high density polyethylene) are preferred materials.

According to the invention, the tank is equipped with a baseplate ormounting plate which is a flattened component (that is to say acomponent the thickness of which is smaller than its length or diameter)intended to blank off an opening in its bottom wall. It should be notedthat this part may be hollow and define a space which communicates withthe tank via an orifice through which the additive can flow.

The baseplate is, in particular, highly suited to supporting accessorieswhich pass through the wall of the hollow body and/or are positionedinside the latter. It has a perimeter that is closed up on itself, ofany shape. Usually, its perimeter is of circular shape.

According to the invention, this baseplate comprises at least oneorifice through which a system for injecting the said additive into theexhaust gases can be fed. This feed may be achieved simply under gravityvia an injection line passing through the baseplate via the saidorifice. Alternatively and as a preference, the system is fed by a pump.

The baseplate also incorporates at least one component that is active instorage and/or injection. What that means is that the component is fixedonto or formed as one with the baseplate. This component may beincorporated inside the tank, or on the outside with, if necessary, aconnection passing through it.

As a preference, the baseplate according to the invention incorporatesseveral components that are active in storage and/or metering and as anespecial preference, it incorporates all the active components whichneed to be in contact with the liquid additive in, leaving or enteringthe additive tank.

As a preference, the component is chosen from the following group: apump; a filter; a level gauge; a heater; a temperature sensor; a qualitysensor; a pressure sensor; a pressure regulator; a venturi tube. Theseelements all have an active part to play in the system for storingand/or injecting the additive, and the fact of incorporating them ontoan “immersed” mounting plate (that is to say a mounting plate that isalways in the additive, provided that the tank is not empty) exhibitsspecific advantages:

-   for the pump: the solution of ammonia precursor can be used to cool    the pump; in the event of freezing, the heat dissipated by the pump    contributes to the return to the liquid state;-   for the level gauge: the lowermost point is better defined and    therefore the measurement is less subject to the influence of    deformations of the tank;-   for the heater: in the event of freezing, the forming of a    compartment through the design of the mounting plate associated with    the heating system allows the volume of additive solution needed to    operate the pollution-reducing system to be delivered within the    time frame required by motor manufacturers (for example: 100 ml in    three minutes);-   for the temperature sensors, quality sensors or sensors that sense    other characteristic(s) of the additive: these can easily be    situated in the critical region in terms of feeding the injection    system;-   for the venturi tube: it becomes heated while the precursor is being    defrosted in the event of low temperatures, ensuring that this    component retains its functionality.

The level gauge, which may be incorporated into the baseplate accordingto the invention, may be of any type. Preferably, it is a gauge with nomoving parts, for example of the capacitive type.

As for the heating, it may comprise a heat exchanger of given capacity,or a heating element, preferably surrounded by or surrounding a space(to create the aforementioned compartment). As a preference, this spaceis of one piece (moulded as one, as appropriate) with the baseplate.Also as a preference, the heater comprises a flexible componentexhibiting a multilayer structure consisting of a resistive elementinsulated between two layers of elastomer (silicone for instance). Theuse of a flexible heater allows it to be adapted to suit a great manybaseplates. In particular, in the event that the baseplate comprisesnipples, the heater is equipped with tabs which can be inserted insidethe nipples of the baseplate thus avoiding plugs from forming at lowtemperatures if the solution of precursor freezes.

The temperature and quality sensors may also be of any known type. Anyother sensor used to measure a characteristic of the additive (purity,concentration, etc.) is suitable for use with the invention.

The present invention also relates to a feed system for feeding a liquidadditive into the exhaust gases of an internal combustion engine, thesaid system comprising a storage system as described hereinabove and aninjection system for injecting the said additive into the engine exhaustgases. This injection system comprises at least one injection line andone injector (that is to say a device for dispersing/nebulizing theliquid additive in the exhaust gases). This injector may be an activeinjector, controlled for in-situ metering of the additive, or a passiveinjector the role of which is confined to nebulizing the quantity ofadditive metered by a suitable device located upstream (generally ametering pump or valve).

The feed system according to the invention may or may not comprise apump for conveying the additive from the additive tank to the injector.As a preference, it comprises a pump (in order to be able to generate astable injection pressure) and in a preferred variant, this pump isfixed to the baseplate. This pump may be situated inside the additivetank (with the advantage that they together constitute a compactintegrated module) or, given the corrosive environment, may be situatedoutside the additive tank. The materials of which it is made willpreferably be chosen from metals that are able to resist corrosion(certain grades of stainless steel and of aluminium in particular).Recourse to copper, even for connectors, is not desirable. The pumpdraws liquid additive from a point known as the tapping-off point in theadditive tank. This point is connected to the pump by a line known asthe pumping line. This point is preferably situated near or even on thebaseplate.

The amount of additive delivered by the pump and not consumed by theinjector (depending on the control from the control unit), if any, isadvantageously returned to the additive tank by a line known as theadditive return line. This line is generally equipped with a pressureregulator and/or with a pressure sensor. It connects either the injectoror some other point on the injection line downstream of the pump to theadditive tank. In this variant, advantageously, the pressure regulatorand/or sensor is/arc preferably also incorporated into the baseplate,that is to say fixed onto the latter, preferably inside the tank.

The feed system according to the invention preferably also comprises afilter, which is, as an especial preference, also incorporatedinto/fixed onto the baseplate. This filter may be situated upstream ordownstream of the pump. When situated upstream of the pump, the filterprotects the pump. As a preference, it is situated downstream of thepump so as to avoid pressure drops and cavitation phenomena.

The baseplate may also comprise at least one nipple for conveying thesolution of urea precursor to the injector. In the event that areturn-to-tank line is provided, a second nipple may be provided.

Depending on the purge system adopted for the lines and on thecomponents connected thereto, provision may be made for the baseplate tobe equipped with bowls/siphons which prevent the liquid from returningfrom the tank to the pipework, or with any other device performing thesame function. Indeed, although in general the pump places the pipeworkunder a certain pressure, which generally prevents such return, the headof liquid in the tank may, in some cases, be enough to overcome thispressure and in spite of everything cause a small stream of liquid toflow towards the pipework. Equipping the orifice of orifices thatprovide the communication between the tank and the pipework withappropriately sized bowls/siphons makes it possible to avoid thisphenomenon.

In response to the geometric constraints on the tank which are imposed,in particular, by the vehicle environment, the baseplate may be equippedwith a trap which creates a reserve of liquid that can be tapped offdepending on the orientation of the vehicle. If need be, the baseplatemay incorporate a device (for example of the venturi type which may beconnected after the nipple in the return line) allowing the trap to befed from a tapping-off point situated in the tank.

Usually, the feed system according to the invention comprises a controlunit either connected directly to the injector (in the case of an activeinjector) or connected to a separate metering device (in the case of apassive injector) and allowing the required amount of additive to beinjected into the exhaust gases (the amount being dependent inparticular on the following parameters: level of emission and conversionof NO_(x); temperature and pressure; engine speed and load; etc.).According to the invention, advantageously, the baseplate and/or thecomponent incorporated into the latter comprises a connection to thiscontrol unit.

The control unit involved in this variant may be the engine control unit(ECU) or some other control unit incorporated into the vehicle (forexample the fuel system control unit (FSCU)). It may equally be aspecial-purpose control unit receiving instructions/information from theECU, from the FSCU or from some other control unit incorporated into thevehicle.

The present invention also relates to a method for manufacturing asystem as described hereinabove. In particular, it relates to a methodfor manufacturing the storage tank of this system.

This tank may be produced by any processing method known for hollowbodies. One preferred procedure, particularly when the tank is made ofplastic, and in particular when it is made of HDPE, is theextrusion/blow-moulding method. In this method, a parison (in one ormore parts) is obtained by extrusion, and is then shaped in a mould byblow-moulding. Moulding the tank as one piece from a single parisonyields good results.

The immersed baseplate of this tank may also be obtained by any knownmeans, but as a preference it is obtained by injection moulding, thismethod making it possible to obtain good dimensional accuracy.

As a preference, the baseplate is based on a material able to resistaqueous solutions of ammonia precursor, such as polyacetal and, inparticular, POM (polyoxymethylene); polyphtalamides (AMODEL® resins forinstance); or polyamides (for example nylon-6,6) and, in particular,reinforced grades (for example glass-fibre-reinforced plastics).

As a preference, the baseplate is provided with attachment systems forthe active components that it is to incorporate. These systems may bemoulded as one with the baseplate or inserts needed for this purpose maybe added during the moulding process (using overmoulding for example) orafter the moulding process (using welding). When the heater comprises aflexible film, this is attached using clips (injected for example innylon-6,6,) which are inserted in the holes in the mounting plate and inthose in the heater which correspond to the former holes.

The opening in the bottom wall of the tank may be produced by anyappropriate means, for example by machining the moulded tank. As apreference, its periphery has a relief (a protrusion with a screw threadfor example) to make it easier to attach the baseplate, and which ismoulded at the same time as the tank.

The baseplate may also be assembled with the opening in the tank by anyknown means, particularly using a ring-nut system screwed onto a threadon the tank side, this thread preferably being produced during theblow-moulding of the tank (through a suitable shape of mould) or using aclosure system of the bayonet type. A gasket (preferably made ofelastomer, NBR or EPDM, for example) preferably provides a seal betweenthe edge of the opening in the tank and the baseplate. As a preference,this gasket rests on a channel formed around the periphery of thebaseplate and is preferably compressed between the periphery of theopening in the tank and the baseplate.

The present invention is illustrated nonlimitingly by FIGS. 1 to 4 whichillustrate a number of preferred variants thereof.

FIG. 1 shows a baseplate [1] fixed to the bottom face of an additivetank (not depicted) and comprising a support [10] allowing the assemblyof a pump [3], a preloaded valve [7] and a filter [8]. In this example,the pump is a gear pump [6] and is turned by an electric motorcomprising a magnet [4] and a coil [5]. The baseplate [1] also comprisesa nipple [9] connected to a pipe connected to an injector or nozzle (notdepicted) for spraying the additive (solution of ammonia precursor suchas urea for example) into the exhaust system (not depicted). Theassembly is surmounted by a heating element [11] allowing the system tooperate at low temperatures (to thaw the ammonia precursor).

This assembly has at least two operating modes: an injection mode and apurge mode.

In the injection mode, the task is to spray the solution of ammoniaprecursor into the exhaust system of the vehicle. To do that, the pump[3] is activated so as to allow it to draw the solution contained in thetank up through the orifice [2]. The fluid than passes through thefilter [8] and is conveyed by the nipple [9] to the pipe that isconnected to an injector or to a nozzle. The raised pressure needed fora good quality spray is controlled by the preloaded valve [7].

In purge mode, the task is to drain the injector, the pipework, thefilter and the volume in which the gear system of the pump is located.

The injector or a purge valve situated on the pipe connected to thenipple [9] is opened. The pump [3] is then activated in such a way as todraw liquid from the injector or the nozzle and deliver it back to thetank via the orifice [2]. A device of the bowl [13] and siphon [12] typeprevents liquid from returning to the purged volume when the pump isstopped.

In the variant illustrated in FIG. 2, the electric motor [4, 5] isincorporated under the baseplate [1], outside the tank. By comparisonwith the preceding example, electrical connection (supply cord [14]) maybe easier.

In the variant illustrated in FIG. 3, in addition to the components andfunctionalities illustrated in FIGS. 1 and 2, the baseplate [1]incorporates a level sensor [15] and a temperature probe [16].

FIG. 4 gives the example of a baseplate mounting plate [1] on which afilter [8], a gear pump [6] actuated by a brushless motor and a pressureregulator [7] are assembled. The mounting plate [1] has a feed nipple[9] and a nipple [10] connected to the injector return line, able totake a purge valve. The mounting plate [1] is equipped with a heatingelement [11] consisting of a flexible sheet of multilayer structure andfixed to the mounting plate by a series of clips [11 a]. The heatingelement [11] has extensions [11 b] which rest on the bottom of the tank[11 c], allowing an additional volume of ammonia precursor to be thawed.The liquid returns from the tank to the baseplate through openings [13]made in the mounting plate [1]. The flexible heater [11] is designedwith heating tabs [11 d] inserted into the nipples [9] and [10] toprevent a solid plug from forming if the solution of precursor freezesinside the nipples [9] and [10].

1. (canceled)
 2. A baseplate comprising at least one orifice throughwhich a system to inject an additive into exhaust gases is feedable andwherein said baseplate further comprises a bottom portion and a verticalwall extending perpendicular to said bottom portion and said base plateincorporates a heater wherein at least a portion of the heater extends,at least partially, in contact with the vertical wall extendingperpendicular to said bottom portion.
 3. The baseplate according toclaim 2, which further incorporates a level gauge.
 4. The baseplateaccording to claim 2, which further incorporates a sensor used tomeasure a characteristic of the additive.
 5. The baseplate according toclaim 4, wherein said sensor is a temperature sensor.
 6. The baseplateaccording to claim 4, wherein said sensor is a quality sensor.
 7. Thebaseplate according to claim 4, wherein said sensor is a pressuresensor.
 8. The baseplate according to claim 2, which furtherincorporates a pump.
 9. The baseplate according to claim 2, whichfurther incorporates a filter.
 10. The baseplate according to claim 2,which further incorporates a pressure regulator.
 11. The baseplateaccording to claim 2, which further incorporates at least one componentselected from the group consisting of a pump, a filter, a level gauge, asensor used to measure a characteristic of the additive, and a pressureregulator, wherein at least a portion of the heater extends, at leastpartially, in contact with said at least one component.
 12. Thebaseplate according to claim 2, wherein a system to inject said additiveinto exhaust gases is connected to said at least one orifice, whereinsaid system comprises least one injection line and one injector.
 13. Thebaseplate according to claim 12, wherein a pump is fixed to saidbaseplate and is connected to said system.
 14. The baseplate accordingto claim 13, wherein a filter is incorporated into or fixed onto thebaseplate and is connected to said system.
 15. The baseplate accordingto claim 12, wherein the baseplate incorporates a nipple to convey aliquid additive to at least one of the injector and a nipple to returnunused liquid additive to the tank.
 16. The baseplate according to claim2, wherein the baseplate further comprises a connection to a controlunit for said system such that the connection is between the baseplateor a component incorporated therein to said control unit.
 17. Thebaseplate according to claim 2, wherein the baseplate includes a bottomplate, at least one wall that intersects the bottom plate, and at leastone support structure projecting inwardly from the at least one wallthat intersects the bottom plate, and wherein the at least one supportstructure supports at least one of the injection system and the at leastone other active component.
 18. The baseplate according to claim 2,wherein the baseplate is made of a material of at least one ofpolyacetal and polyamide.
 19. The baseplate according to claim 2,wherein the baseplate has a thickness that is smaller than its length ordiameter.